Pancake Ice

 
On our hike Saturday we saw these strange formations in the ice at the edge of Hamlin Lake. The largest circle is about a foot across.



I've been trying to find out what causes these circles. My best guess is a phenomenon called "ice pans," or "pancake ice." These are slightly different from the large rotating ice circles that sometimes form in river bends. These form in still water. The description on Wikipedia of how they form doesn't really work for me with the end result, so I'm not going to try to explain it.

However, if you look closely, some of these do have the elevated rims that pancake ice should have. Those rims are formed of frazil ice. There's a new word. It's a type of slushy ice with loose long crystals in it. And they form when the temperature takes a sudden drop. That was true last week too.

Looking back, I see that I actually had a good picture of a loose ice pancake on the Muskegon River last winter. In fact, I called that post Cold Cakes. It must have formed in a slow-moving eddy and then broken loose.

My guess is that these formed when the wind was moving the water around, and then when the wind died down they froze together.

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